[PATCH] Avoid unnecessarily re-allocating texture buffer when the size hasn't changed.

[Sinclair Yeh]

Depending on specific DRI driver implementation, glTexImage2D() with data
set to NULL may or may not re-allocate the texture buffer each time it is
called.  Unintended consequences happen if later glTexSubImage2D() is called
to only update a sub-region of the texture buffer.

I've explored moving glTexImage2D() from gl_renderer_attach() and simply
mark the texture dirty, but the current implemention seems cleaner because
I won't have to worry about calling ensure_textures() and re-assigning
gs->shader unnecessarily.
---
 src/gl-renderer.c |   32 ++++++++++++++++++++------------
 1 files changed, 20 insertions(+), 12 deletions(-)

diff --git a/src/gl-renderer.c b/src/gl-renderer.c
index be74eba..78e9a94 100644
--- a/src/gl-renderer.c
+++ b/src/gl-renderer.c
@@ -68,6 +68,7 @@ struct gl_surface_state {
 
 	struct weston_buffer_reference buffer_ref;
 	int pitch; /* in pixels */
+	int height;
 };
 
 struct gl_renderer {
@@ -1213,18 +1214,24 @@ gl_renderer_attach(struct weston_surface *es, struct wl_buffer *buffer)
 	}
 
 	if (wl_buffer_is_shm(buffer)) {
-		gs->pitch = wl_shm_buffer_get_stride(buffer) / 4;
-		gs->target = GL_TEXTURE_2D;
-
-		ensure_textures(gs, 1);
-		glBindTexture(GL_TEXTURE_2D, gs->textures[0]);
-		glTexImage2D(GL_TEXTURE_2D, 0, GL_BGRA_EXT,
-			     gs->pitch, buffer->height, 0,
-			     GL_BGRA_EXT, GL_UNSIGNED_BYTE, NULL);
-		if (wl_shm_buffer_get_format(buffer) == WL_SHM_FORMAT_XRGB8888)
-			gs->shader = &gr->texture_shader_rgbx;
-		else
-			gs->shader = &gr->texture_shader_rgba;
+		/* Only allocate a texture if it doesn't match existing one */
+		if (((wl_shm_buffer_get_stride(buffer) / 4) != gs->pitch) ||
+		    (buffer->height != gs->pitch)) {
+			gs->pitch = wl_shm_buffer_get_stride(buffer) / 4;
+			gs->height = buffer->height;
+			gs->target = GL_TEXTURE_2D;
+
+			ensure_textures(gs, 1);
+			glBindTexture(GL_TEXTURE_2D, gs->textures[0]);
+			glTexImage2D(GL_TEXTURE_2D, 0, GL_BGRA_EXT,
+				     gs->pitch, buffer->height, 0,
+				     GL_BGRA_EXT, GL_UNSIGNED_BYTE, NULL);
+			if (wl_shm_buffer_get_format(buffer) ==
+			    WL_SHM_FORMAT_XRGB8888)
+				gs->shader = &gr->texture_shader_rgbx;
+			else
+				gs->shader = &gr->texture_shader_rgba;
+		}
 	} else if (gr->query_buffer(gr->egl_display, buffer,
 				    EGL_TEXTURE_FORMAT, &format)) {
 		for (i = 0; i < gs->num_images; i++)
@@ -1279,6 +1286,7 @@ gl_renderer_attach(struct weston_surface *es, struct wl_buffer *buffer)
 		}
 
 		gs->pitch = buffer->width;
+		gs->height = buffer->height;
 	} else {
 		weston_log("unhandled buffer type!\n");
 		weston_buffer_reference(&gs->buffer_ref, NULL);
-- 
1.7.7.6